Heretofore, short-haul lightguide transmission systems, i.e., those covering distances of up to about 10 kilometers, have employed directly modulated lasers or light-emitting diodes (LEDS) in tandem with multimode lightguides having an attenuation of approximately 1-2 db per kilometer. On the other hand, long-haul lightguide transmission systems, i.e., those covering distances of up to about 40 kilometers, have employed directly modulated lasers driving single-mode lightguides having an attenuation of approximately 0.5 db per kilometer. Single-mode fibre is usually characterized by a central core having a diameter of about 8 microns. Directly modulated lasers are those wherein the drive current to the laser is itself directly subjected to a modulating signal. Since the single mode fibre system achieves its efficiency only when driven by the more expensive laser rather than by light emitting diodes which provide multimode emission, it has not priorly been economical to employ single mode fibre and directly modulated lasers in the local plant.